Abstract: In order to improve optical processing speed and the feasibility of optical realization in interference encryption technology, based on the idea of interference encryption principle and image processing method of grating filter, 4f system double image optical encryption technology based on grating filter was designed. The mature image additiion and subtraction 4f system based on grating filtering was used to transform two encrypting images into two real values of white noise. The feasibility and effectiveness of the method were verified by theoretical simulation. The results show that the method is simple, practical, safe and easy to implement.